It is proposed to design complexes containing transition metals bound to simple macrocyclic ligand systems. These complexes will be used: (1) as models to examine the details of reaction mechanisms of general interest or which seem to be significant in complex biological systems; (2) in attempts to model in simple systems reactions of metallo enzymes which seem to have little or no precedent in simpler inorganic systems. Where possible reactions of the prosthetic groups of metallo enzymes will be examined under the conditions of the model reactions.